The possibility of future electrical energy shortages requires that considerable attention be given to conservation measures. As electricity for lighting is almost universally used, conservation of electricity in this area could result in considerable savings of energy.
Parallel uses of glass and higher levels of artificial illumination have been modern trends by architects. However, effective utilization of natural light played little or no part in the design of building illumination systems.
Most modern buildings have the lighting zones broken down so one switch controls a 1,000 to 1,600 watts of lighting fixtures on a 110 volt 60 cycle electrical supply. A zone can be broken into sub-loops. If the sub-loop fixtures are properly oriented within a zone, perhaps an office, natural outside light can serve as a base and artificial light can be supplemented as needed to maintain a desired level of illumination as solar light varies. However, to be effective, such a lighting system must have an automatic control for blending the natural and artifical light.
Prior light control systems have been developed such as that shown in U.S. Pat. No. 1,944,751 wherein a relay controlled by a photo-sensor device adds or removes impedance of associated lighting units so that the lighting units are always operated at their rated power values. While such a system detects the illumination level in a room, such a system lacks the sophistication required for continuous blending of interior artificial light with natural light from the sun in an efficient manner. Likewise, such a system does not provide for detecting erroneous illumination levels such as when light bulbs are burned out and sufficient lighting to maintain the desired illumination level is not available.